This invention relates to a process and apparatus for the liquefaction of coal, and, more particularly, to the treatment of the effluent obtained by such liquefaction.
In particular, the invention relates to coal liquefaction processes wherein a solvent (hereinafter sometimes called liquefaction solvent) is present during the liquefaction of the coal. Liquefaction may be achieved by hydrogenation, depolymerization, extraction, etc. The liquefaction solvent, which is generally coal-derived, may function as solvent for the coal or for the products, or both. It may also play a reactive role, for instance, in the depolymerization and hydrogenation of the coal molecules. Liquefaction may also be achieved with or without the presence of a catalyst, and with or without the presence of molecular (gaseous) hydrogen, in addition to the liquefaction solvent. Examples of such coal liquefaction processes are described in U.S. Pat. Nos. 3,018,242; 3,177,921; 3,143,489; 3,158,561; 3,523,886; U.S. Pat. No. Re. 25,770; and No. 3,321,393.
The product effluent from such coal liquefaction processes is a mixture of liquid and undissolved solids. Distillation of the effluent will produce three essential product streams. Of the volatile material, part will be recovered as solvent to be recycled to the coal extractor. A second part of the distillate can be considered the product distillate. Further refinement of this product distillate will yield various gaseous or liquid fuels, chemicals, or chemical precursors. The third product is the non-volatile extract and residual solids. This material is suitable as a feedstock for gasification or coking. The difficulty with the solvent extraction coal liquefaction processes lies in the fact that, having removed the lower molecular weight volatiles, the "still bottoms" will comprise a highly viscous and correspondingly intractable material. The viscosity of the material can be reduced by taking a lower distillate cut, but, of course, with a reduction in the net yield of product distillate.
The primary objective of this invention is to provide a method and apparatus for handling the still bottoms which will both maximize the distillate yield, and produce a solid product useful as a gasifier or coker feedstock.
The following patents were considered in the preparation of this application: U.S. Pat. No. 2,060,447, and South African Pat. No. 75/0044.